Hydrogen diffusion reactor control



United States Patent 3,351,534 HYDROGEN DIFFUSION REACTOR CONTROL RobertMagladry, Baltimore, Md., assignor to Martin- Marietta Corporation, NewYork, N.Y., a corporation of Maryland Continuation of application Ser.No. 374,656, June 12, 1964. This application Jan. 3, 1966, Ser. No.520,824 26 Claims. (Cl. 17642) This is a continuation of my copendingapplication, Ser. No. 374,656, filed June 12, 1964, and entitled,Hydrogen-Diffusion Reactor Control, which application is now abandoned.

The present invention relates to nuclear reactors and more particularlyto the means for regulating and controlling the nuclear reactionoccurring therein comprising a dual function control rod.

The nuclear reaction is controlled in most cases by the insertion orrotation of a regulating or control rod into the composition. This rodcan contain a neutron absorbing material which reduces the nuclearreaction rate, fissionable material which increases the reaction rate,or neutron scattering or moderating material which also increases thereaction rate by increasing the probability that neutrons will causefission before they are lost through nonfission absorption or leakage.Regardless of the nuclear process involved, regulating and controllingof the reaction requires that the control rod be mechanically positionedwithin the reactive composition. The nuclear reactor is operated withthe control rod at or near what is commonly termed the criticalposition. Displacement of the control rod from this position either willprovide a neutron reproduction ratio below unity in which event theneutron density declines or will provide a neutron reproduction ratioabove unity in which event the neutron density in the reactor rises.Apart from obtaining a desired neutron density, the return of thecontrol rod to the critical position acts to hold the reaction at thedesired level. Since such reactors operate with movable mechanicalapparatus to automatically regulate the reactor to the condition ofcriticality during moderate variations in operating parameters, thereactor must be constantly monitored which, of course, involves somemechanical movements. In addition to the employment of means forvariably positioning the control rod with respect to the reactivecomposition, the nuclear reaction may also be partially or totallycontrolled by suitably controlling the movement of fluid to and from thereactive composition of a nuclear reactor. This fluid may also serve asa reactor coolant, but in any case, afiects the nuclear reaction bychanging the probability of neutron absorption, neutron fission, orneutron scattering. Heretofore, these methods of control have requiredmovable mechanical apparatus and associated sensing means for effectingautomatic regulation.

It is, therefore, a primary object of the present invention to providean improved nuclear reactor employing a completely mechanically passivecontrol system.

It is a further object of this invention to provide a control system ofthis type which is inherently self-regulating.

It is a further object of this invention to provide an improved nuclearreactor incorporating a control system which is capable of providingthree modes of reactor power regulation and/or control involving:

(1) the maintenance of an established power level;

(2) a change in power level to maintain a given coolant temperature; and

(3) independent control over power level.

It is a further object of this invention to provide an improved nuclearreactor having a control system of this type which is compatible withconvection cooling of the critical region of the reactor.

Further objects of this invention will be pointed out in the followingdetailed description and claims and illustrated in the accompanyingdrawing which discloses, by way of example the principle of thisinvention and the best mode which has been contemplated of applying thatprinciple.

In the drawing:

The single figure is a schematic view of a nuclear reactor incorporatingthe improved control system of the present invention.

In general, the present system is directed to a selfregulating,mechanically passive control system for a nuclear reactor having as itsmain section a reactive composition of region(s) containing fissionablematerial, that is, reactor fuel, which are commonly termed core and mayhave within this section region(s) containing non-fissionable materialwhich are commonly termed reflector. The control system incorporates acontrol rod of hydride material which is fixed with respect to the mainreactor section such that one end of the rod is positioned internallywithin the section and the other end protrudes exteriorly thereof.Fissionable material, that is, reactor fuel, or other material subjectto nuclear heating is incorporated within the internal end of the rodand means are provided for producing a temperature differential betweenthe internal and external ends of the rods to vary the hydrogenconcentration within respective ends of the rod. More than one controlrod may be utilized in the control system. When these control rodscontain reactor fuel, they also serve as reactor fuel elements in theconventional sense.

Referring to the drawing, there is shown schematically the nuclearreactor having a main section 10, as is conventional in the art,including suitable core and reflector means, indicated generally bynumerals 12 and 14, respectively. The control system of the presentinvention has broad application to most conventional nuclear reactorsystems and employs principally one or more control elements in whichpenetrate either the core or reflector portion of the main reactorsection 10 having a portion 18 internally of the reactor and a portion20 extending exten'orly thereof. The element 16 is formed of hydridematerial and the control function is broadly achieved by varying thehydrogen concentration within the control element 16 and utilizing theeffect upon the reaction occurring within the main section of thenuclear reactor. Specifically, the moderation of the nuclear reaction isincreased or decreased according to whether the hydrogen concentrationin the main section is high or low. Hydrogen has the highest property,cross-section, for the scattering of neutrons of any known chemicalspecies. Neutron diffusion velocities are considerably reduced by thescattering process and, thereby, the probability of the neutrons leakingfrom the main section of the reactor is reduced. The nuclear reactionrate is, in turn, dependent upon the retention of neutrons within thereactive composition. Suitable hydride materials, that is, materialswhich can retain hydrogen within their structure within a conventionalnuclear reactor environment, are yttrium, zirconium, silicon, niobium,calcium, and barium. The hydride material can be alloyed or otherwisecombined with nuclear fuel material, such as uranium, plutonium andthorium.

In the preferred form, reactor fuel is incorporated in the hydridematerial and the temperature of the internal section 18 of the elementis maintained by the material itself which is susceptible to nuclearheating from the reactor fuel incorporated therein. Thus, thetemperature of the internal section is directly dependent upon thereaction occurring therein. It must be appreciated that the rod providesthe dual function of controlling reaction and supplying fuel forreaction, the functions heretofore never incorporated in a singleelement. In contrast, the temperaa 73 ture of the external section 20 ofthe hydride control element and the temperature differential between theinterior section 18 of the element and the external section 20 can becontrolled by external heating means. The drawing shows, in schematicform, one method for effecting temperature variation in the externalsection 20 of the hydride control element. In the illustrativeembodiment shown, an electrical resistance heater, indicated at 22, isconnected in series with a power source, representatively shown bybattery 24 which may be connected and disconnected through switch 26.The current flow from the source or battery 24 is controlled by a simplerheostat 28 which is connected in series between the power source 24 andthe resistor 22.

As mentioned previously, the control system resides in the fact that thehydride material provides a variable hydrogen concentration withininternal hydride section 18. Change in the temperature of the section 20of the hydride element, which is exterior to the main reactor section,relative to the temperature of the section 18 of the hydride element,which is within the main reactor section, causes the hydrogenconcentration within the main reactor section to either increase ordecrease. Thus, the reactivity of the reactor and consequently thereactor power is thereby either maintained or modified (increased ordecreased).

The temperature level of the element 16 establishes the solubility ofhydrogen in the hydride material. The temperature difference between thetwo sctions 18 and 20 of the element establishes the rate of hydrogendiffusion between the sections. Heat is released by the hydride materialwhen hydrogen is entering solution and heat is absorbed by the hydridematerial when hydrogen is leaving solution. Heat is nominally exchangedbetween the element 16 and the reactor coolant which surrounds theinterior section 18 of the hydride element, through convective coolingof the internal section. The flow path is indicated by arrows 30,passing from inlet 32 to outlet 34. It is obvious therefore that theregulation and/or control of the reactor power may be achieved byarranging the required temperatures under the conditions set forthabove.

While the invention has been described in extremely simplified terms asapplied to a reactor shown only schematically in the drawing, thecontrol system of the present invention may be more readily understoodby a brief description of system operation from the standpoint oftypical operational changes from the desired norm. For instance, anundesired change from a given power level, for instance, a powerincrease, causes the temperature of the internal section 18 of theelement to increase and thereby causes hydrogen to diffuse from theinternal section 18 to the external section 20. The resulting decreasein hydrogen concentration within the internal section of the hydrideelement causes nuclear reactivity to fall below its critical value andconsequently the reactor power to decline. As the internal sectiontemperature declines with the power, the hydrogen diffuses back into itincreasing the hydrogen concentration within the internal section of thehydride element 16 until the reactivity is again at its critical value.The given power level is thereby-reestablished. The converse processoccurs with an undesirable power decrease from a given level. Anincrease in hydrogen concentration will occur within the internalsection increasing nuclear reactivity tending to effect temperature risewith resultant hydrogen diffusion from the internal to the externalsection until the given level again is re-established as a result ofchange in hydrogen concentration.

As mentioned previously, the temperature of the coolant or the relativeflow of coolant and heat absorption thereof greatly affects theoperation of the reactor. For instance, a change in coolant temperaturefrom a given level, such as a temperature increase due to a reducedcoolant flow, causes the temperature of the internal section 18 of theelement to increase, thereby causing diffusion of hydrogen from theinternal to the external section of the element and as a result of thesequence of events set forth previously, results in a reduced powerlevel such that the coolant temperature is returned to its given level.Conversely, a coolant temperature decrease due to increased coolant flowresults in an increased power level which returns the coolanttemperature to its given level.

From the above, it is apparent that not only is the system mechanicallypassive but the system is completely self-regulating.

During startup and shutdown operations, it is desirable to haveindependent control of reactor power. Such independent control iseffected by varying the electrical heating of the external section ofthe element, thereby creating the desirable temperature differentialbetween the internal section 18 and the external section 20 of thehydride element. By changing the rheostat setting, an increase inelectrical power input from battery occurs, which results in increasedheating of resistor heater. The solubility of hydrogen in the internalsection 18 of the element increases as a result of conduction heating ofthe internal section by the external section. Hydrogen diffuses from theexternal section 20 to the internal section 18 increasing the hydrogenconcentration in that section and providing an increase in nuclearreactivity. A decrease in electrical power input operates in a conversemanner, decreasing the internal hydrogen concentration and causing adecrease in nuclear reactivity. Steady state power levels are reachedwhen the hydrogen concentration as a result of the internal nuclearheating and external electrical heating places reactivity at itscritical value.

It is obvious that the simplified control system of the presentinvention which is highly compatible with simple convection cooling ofthe critical region of the reactor provides a mechanically passivesystem which is inherently self-regulating and eliminates the need forcontrol rods, control drums, soluble poisons, etc., normally utilized inthe prior art devices.

The power level of the reactor, of course, is partially controlled bythe amount of heat removed by the coolant surrounding the internalsection 18 of the hydride element. The rate of coolant fiow may bevaried with the coolant subsequently converted to steam within a heatexchanger (not shown) located either externally or internally of themain reactor section 10. Of course, the steam output may be utilized ina conventional manner. for instance, heating, power production, etc.

It it apparent that in the preferred embodiment shown, a simple, compactnuclear reactor is thus provided which requires no attendance sincethere are no moving parts, no mechanical control rods and the reactor isinherently self-regulating. While there have been shown and describedand pointed out the fundamental novel features of the invention asapplied to a preferred embodiment, it will be understood that variousomissions and substitutions and changes in the form and detail of thesystem illustrated and in its operation may be made by those skilled inthe art without departing from the spirit of the invention. It is theintention, therefore, to be limited only as indicated by the scope ofthe following claims.

What is claimed is:

1. A self-regulating, mechanically passive control system for a nuclearreactor having a main reactor section including core and reflectormeans, said system comprising: a control rod of hydride material, saidcontrol rod fixedly positioned with respect to said main reactor sectionwith one end of said rod disposed therein in operative relation to saidcore and reflector means and the other end extending exteriorly of saidcore, reactor fuel incorporated within the end of said rod positionedinternally of said core and means for producing a temperaturedifferential between said rod ends to thereby vary the hydro- 7 genconcentration within respective ends of said rod.

2. The apparatus as claimed in claim 1 wherein said hydride material isa compound selected from the group consisting of yttrium hydride,zirconium hydride, silicon hydride, niobium hydride, calcium hydride,and barium hydride.

3. The apparatus as claimed in claim 1 wherein said reactor fuelincorporated within the end of said rod positioned internally of saidcore is an element selected from the group consisting of uranium,plutonium, and thorium.

4. The apparatus as claimed in claim 1 wherein said means for producinga temperature differential includes an electrical heating elementpositioned in proximity to the end of said control rod exterior of saidcore, means for supplying current to said heating element, and means tocontrol said current flow.

5. The apparatus as claimed in claim 1 wherein said means for producinga temperature differential includes a coolant and means to move saidcoolant within said reactor core in proximity to the inner end of saidcontrol rod whereby heat is absorbed by said coolant through convection.

6. A self-regulating, mechanically passive control system for a nuclearreactor having a main reactor section including core and reflectormeans, said system compris ing: a control rod of hydride material, meansfor fixedly positioning said control rod with respect to said mainreactor section whereby one end of said control rod is disposed thereinin operative relation to said core and reflector means and the other endextends exteriorly of said core, reactor fuel incorporated within theinner end of said control rod, means for directing coolant about theinner end of said control rod to absorb heat therefrom by convection, anelectrical heating element positioned in proximity to the outer end ofsaid control rod exteriorly of said core, a source of electricalcurrent, means for connecting said source of current to said heatingelement and means for varying current flow through said heating elementwhereby a temperature differential is produced between the inner andouter ends of said control rod to vary the hydrogen concentration withinrespective ends of said rod to regulate nuclear reaction occurring inthe critical region of said reactor.

7. An improved nuclear reactor having a main reactor section includingcore and reflector means, a source of coolant within said main reactorsection within the critical region thereof for removing the heat ofreaction by convection, the improvement comprising: a control rod ofhydride material, said control rod being fixedly positioned with respectto main reactor section with one end of said control rod disposed withinsaid main reactor section in operative relation to said core andreflector means and in contact with said coolant and the other end ofsaid control rod extending exteriorly thereof, reactor fuel incorporatedwithin the internal end of said rod, and means for producing atemperature differential between the internal and external ends to varythe hydrogen concentration within respective ends to provide aself-regulating, mechanically passive control system.

8. The apparatus as claimed in claim 7 wherein said means for producinga temperature differential includes an electrical resistance heaterpositioned in proximity to said external end of said rod, means forconnecting a source of electrical current to said electrical heater andmeans for varying said current flow.

9. A nuclear fuel control rod for a nuclear reactor employing aself-regulating, mechanically passive control system including a mainreactor section having core and reflector means with a portion of saidrod fixedly positioned within said core means and a portion extendingexteriorly thereof, with means for modifying the temperature of saidexterior portion, said inner portion of said rod comprising an alloy ofhydride material and nuclear fuel material and said outer portion ofsaid rod comprising pure hydride material.

10. The device as claimed in claim 9 wherein said hydride material is acompound selected from the group consisting of yttrium hydride,zirconium hydride, silicon hydride, niobium hydride, calcium hydride,and barium hydride.

11. The device as claimed in claim 9 wherein said nuclear fuel materialis an element selected from the group consisting of uranium, plutonium,and thorium.

12. A self-regulating, mechanically passive control system for a nuclearreactor having a main reactor section including core means carrying fuelmaterial and reflector means, said system comprising: a control rod ofhydride material, said control rod fixedly positioned with respect tosaid main reactor section with one end of said rod disposed therein inoperative relation to said core means and the other end of said rodextending exteriorly thereof, and means for modifying the temperature ofsaid rod end exterior of said core means to vary the hydrogenconcentration within respective ends of said rod.

13. The apparatus as claimed in claim 12 wherein said hydride materialis a compound selected from the group consisting of yttrium hydride,zirconium hydride, silicon hydride, niobium hydride, calcium hydride,and barium hydride.

14. The apparatus as claimed in claim 12 wherein said means formodifying the temperature of one end of said rod comprises electricalheating means positioned in proximity to the end of said control rodexterior of said core, means for supplying electrical current to saidheating element and means to control said current flow.

15. A device for controlling a nuclear reactor having a core zonecomprising:

(a) a control rod of hydride material having a first end adapted to bepositioned within said core zone; and

(b) means for controlling the temperature of the other end of saidcontrol rod independently from its environment and said first end toeffect a temperature differential between said ends of said control rod,whereby the hydrogen concentration within said respective ends isdependent upon said temperature differential.

16. The device of claim 15 wherein reactor fuel is incorporated in saidfirst end of said control rod.

17. A device for controlling a nuclear reactor having a core comprising:

(a) a member of hydride material having a first section positioned inoperative relationship with the reactor core; and

(b) means for controlling the temperature of a second section of saidmember independently from its environment and said first section wherebya differential in hydrogen concentration is effected between saidsections dependent upon the temperature differential between saidsections.

18. A device of claim 17 wherein reactor fuel is incorporated in saidfirst section of said member.

19. A device for controlling a nuclear reactor having a core zonecomprising:

(a) a member of hydride material having a first section positionedwithin said core zone;

(b) first means for initially increasing the temperature of a secondsection of said member relative to said first section whereby hydrogendiffuses from said second section to said first section to initiateoperation of said reactor; and

(0) second means for subsequently varying said temperature differentialas a function of changes in the temperature of the core of said reactor.

20. A device for controlling a nuclear reactor having a core zonecomprising:

(a) a member of hydride material having a first section positioned insaid core zone; and

(b) electrical heating means operable with a second section of saidmember to increase the temperature of said second section with respectto the temperature of said first section of said member, wherebyhydrogen is caused to diffuse from said second section to said firstsection.

21. A device for controlling a nuclear reactor having a core zonecomprising:

(a) a member of hydride material having a first section positionedwithin said core zone;

(b) first means for effecting an initial hydrogen concentrationdifferential between the first and a second section of said member; and

() means for subsequently effecting diffusion of hydrogen reversiblybetween said first section and said second section as a function ofsubsequent changes in the temperature of said core.

22. A device for controlling a nuclear reactor having a core zonecomprising:

(a) a hydride member positioned Within said core zone,

the hydrogen content of said member being insufiicient to produce thecritical state within said reactor;

(b) means for initially increasing the hydrogen content of said hydridemember to effect a critical state within said reactor; and

(c) means for subsequently varying the hydrogen content of said hydridemember as a function of the temperature of said core.

23. A device for controlling a nuclear reactor having a core zonecomprising:

(a) hydride means having a first section adapted to be positioned withinsaid core zone and a second section adapted to be positioned externallyof said core zone, said first section communicating with said secondsection whereby hydrogen can flow therebetween; and

(b) means for controlling the temperature of said second sectionindependently from its environment and said first section.

24. The device of claim 23 wherein reactor fuel is incorporated in saidfirst section.

8 25. A device for controlling a nuclear reactor'having a core zonecomprising:

(a) hydride means having a first section adapted to be positioned withinsaid core zone and a second section adapted to be positioned externallyof said core zone, said first section communicating with said secondsection whereby hydrogen can flow therebetween; and

(b) a heating means operable with said second section to increase thetemperature thereof with respect to the temperature of said firstsection, whereby hydrogen is caused to diffuse from said second sectionto said first section.

26. A device for controlling a nuclear reactor having a core zonecomprising:

(a) a member of hydride material positioned within said core zone; (b) ahydrogen source external to said core zone and communicating with saidmember; and (c) means to induce reversible hydrogen flow between saidsource and said member.

References Cited UNITED STATES PATENTS 2,952,600 9/1960 Newson 176862,976,227 3/1961 Wheeler 176-42 2,998,367 8/1961 Untermyer 176423,164,525 1/1965 Wetch et a1. 176--42 3,218,236 11/1965 Tollet 176843,285,822 11/1966 Ackroyd 176-42 FOREIGN PATENTS 1,355,945 2/1964France.

913,168 12/1960 Great Britain.

OTHER REFERENCES Nucleonics, vol. 14, No. 11, November 1956, pages146-153.

L. DEWAYNE RUTLEDGE, Primary Examiner.

26. A DEVICE FOR CONTROLLING A NUCLEAR REACTOR HAVING A CORE ZONECOMPRISING: (A) A MEMBER OF HYDRIDE MATERIAL POSITIONED WITHIN SAID COREZONE; (B) A HYDROGEN SOURCE EXTERNAL TO SAID CORE ZONE AND COMMUNICATINGWITH SAID MEMBER; AND (C) MEANS TO INDUCE REVERSIBLE HYDROGEN FLOWBETWEEN SAID SOURCE AND SAIID MEMBER.